Hinduism has always considered Lord Vishnu as narayan or Hari. All incarnations (avatars) of Vishnu are also considered as narayan as well, such as Ram Narayan or Krishna Narayan. Most of us have also seen Narad Muni saying “Narayan Narayan” in many TV serial, by saying “Narayan Narayan”, Narad Muni remembers his supreme lord Vishnu.
In Hinduism, there are 4 main yugs: Satya Yug, Treta Yug, Dwapar Yug and Kali Yug. Currently, humans are living in Kali Yug. In past, there were many people who called themselves god/bhagwan, and many will take birth and call themselves god, but one should understand god.